How did you get the response? By mail? Or just in-game. Interestingly enough, going the route described mentioned in the response will ask you to point out the item you're missing, which could be kind of difficult...I raised a ticket and got this response.
“ We are aware of an issue may prevent players from receiving more than one item in any Undaunted Reward Box from the following dungeons:
Bedlam Veil
Oathsworn Pit
Bal Sunnar
Scrivener's Hall
This does not impact event tickets. If you experience this issue, reach out to customer support for assistance. After selecting your platform, select "I have an item issue", then "Missing Item".”
Which is exactly the way I raised the ticket I got this response to… Am I caught in a loop?